The present invention relates in general to orthopedic implements and in particular to rasps for preparing the medullary canal of a bone for receiving a prosthesis implant. More specifically, the present invention relates to the design of an adjustable handle for a femur bone rasp.
Prior to the implant of a prosthesis which is designed to be inserted into the top of the femur and seat within the medullary canal, such as when performing a total hip replacement, the orthopedic surgeon must prepare the medullary canal for the prosthesis. Preparation of the femur canal for receiving the implant involves the use of a bone rasp with a blade portion whose shape is similar to the shape of the prosthesis portion inserted into the femur. The bone rasp also includes a detachable handle and although the rasp handle may be fixed to the blade as an intergral unit, it is more likely and preferred for the handle to be removable by means of a manually releaseable mechanical attachment.
The detachable rasp handle typically extends well above the end or head of the rasp blade and the enlarged head of the handle is normally struck by the orthopedic surgeon by means of a mallet. The striking force is significant but is necessary in order to clean out the medullary canal and shape it correctly for receipt of the prosthesis. It is common for the rasp to be designed for the specific patient taking into consideration the size, shape and orientation of the femur as well as related anatomical aspects.
Typically the rasp blade has a body portion which is of relatively uniform width in a first longitudinal geometric plane and is tapered in the other or second longitudinal geometric plane which is normal to the first plane. In this second geometric plane, the body portion of the rasp blade extends in a proximal direction relative to the femur, bending at an angle of between 40 and 60 degrees as it extends into and terminates in the head of the rasp blade portion. The head has an angled surface in this second geometric plane against which the rasp handle seats. By means of a sliding and interlocking fit the handle is secured to the head of the rasp blade. The handle typically includes an attaching portion and at a fixed angle of incline relative thereto in this first geometric plane, a handle shaft portion. The angles of incline of the blade portion and handle portion in this second geometric plane are such the longitudinal axis of the rasp blade is substantially parallel with the longitudinal axis of the handle shaft portion. Consequently, when the rasp blade is oriented in a substantially vertical fashion, the handle shaft will be substantially vertical as well.
Conventionally, it is preferred to have the handle shaft in a substantially vertical orientation so that the striking action of the mallet by the orthopedic surgeon will not glance off or introduce undesirable angled force vectors. It is desired for the rasp blade and handle shaft to be coplanar in the first geometric plane which is substantially normal to the second geometric plane referenced above.
While the coplanar configuration can generally be achieved independent of the specific femur size, shape and orientation, it is not always possible to achieve a vertical orientation for the handle shaft in the second geometric plane as referred to above. Whenever the anatomy of the femur causes the rasp blade portion to be inserted at an angle off of vertical, such as in order to clear the cut head of the femur, what results is an orientation of the handle shaft at an angle off of vertical. This angle may be either plus or minus (clockwise or counterclockwise) relative to vertical and may be as much as 15 to 20 degrees in either direction. Since the amount of shift off of vertical for each patient can be predetermined by means of x-rays, it is possible to make each femur bone rasp a custom made design in order to keep the handle shaft on the vertical axis even when the anatomy of the femur canal is off of vertical. The custom making of a rasp for each patient is a relatively expensive option and requires more lead time for design and custom manufacturing before the prosthesis can be implanted.
If the rasp handle can be made adjustable relative to the rasp blade then a somewhat standardized rasp blade and handle could be provided and would be suitable for a larger number of patients. As the orientation of the rasp blade relative to the femur shifts from patient to patient, the handle portion would simply be manually pivoted in either a clockwise or counterclockwise direction for the specific patient thereby re-establishing a near vertical orientation for the rasp handle shaft. The present invention is directed to providing such an adjustable rasp handle.
While a variety of rasps and rasp handle designs are known to exist, none of these designs provide the adjustability which is the focus of the present invention. However, consideration of the corresponding patent references may be of interest to appreciate the types of rasp designs which have been conceived of over the years. These patent references include the following:
______________________________________ Patent Numbers Patentee Issue Dates ______________________________________ 4,739,750 Masse 4/26/88 Des. 273,806 Bolesky 5/08/84 Des. 272,648 Bolesky 2/14/84 4,306,550 Forte 12/22/81 4,552,136 Kenna 11/12/85 4,919,679 Averill 4/24/90 3,815,599 Deyerle 6/11/74 4,990,149 Fallin 2/05/91 4,601,289 Chiarizzio 7/22/86 4,583,270 Kenna 4/22/86 4,671,275 Deyerle 6/09/87 Fr. 2547-192A France (Lahille) 5/18/83 4,765,328 Keller 8/23/88 4,587,964 Walker 5/13/86 ______________________________________
As can be appreciated from a consideration of these various references, they disclose a variety of rasp blade and handle designs many of which are intended for cleaning out and preparing the medullary canal of a bone for the implant of a prosthesis. While some of the references such as Masse disclose adjustability, it discloses adjustability as to the spacing or sizing of the rasp blade portion due to the design of a split blade. Other references such as Bolesky ('806) disclose the offset configuration between the blade portion and the handle portion including the enlarged head which is typically struck by the orthopedic surgeon. This particular design also reveals the detachability between the handle and the rasp blade, in this instance by means of a mechanical attachment. Other references such as the patent to Forte illustrate what might incorrectly be interpreted as a joint of adjustability between the head of the rasp blade and the handle, specifically, item 64 as illustrated in FIG. 1. However, drawings can be misleading and item 64 is simply a transverse slot and does not provide any type of universal connection nor handle adjustability. The device disclosed in Fallin is believed to be typical of the design mentioned regarding the manner of releasing the handle portion from the head of the rasp blade. In this particular design the rasp blade has a generally cylindrical bore into which a pin on the handle is inserted. This pin is spring loaded such that by means of a trigger at the upper end of the handle the pin can be released from the rasp blade in order to separate these two components. As is clear from the design details illustrated and described in the Fallin patent there is no disclosure of nor any means provided for making the connection adjustable.
The lack of any handle adjustability in order to standardize the rasp design for a wider range of patients and still be able to maintain the desired verticality of the handle, is clear from a review of the listed patent references. The French patent in the name of Lahille discloses a hollow rasp with its stem formed by two parts. These two parts are locked into position on the fixed stem portion and thereby create the hollow interior. The focus of this invention, which does not include any handle adjustability, is directed to using the hollow interior for a collection of bone material which is removed from the interior of the femur so as not to clog the teeth of the rasp.